Dengue Prevention in BCS

Mosquito3Dengue Fever – Symptoms and Prevention

Download PDF: 2013 Dengue in BCS copy

Over 2,000 cases of Dengue Fever have been reported in Baja California Sur the past few years. Highest percentage of reported cases are in Cabo San Lucas. Putting it in perspective the same region is home to more than half a million residents and visitors.

Residents have been urged to clean up standing water in their yards, putting screen on septic vents and to make sure their tinacos (water cisterns) are bug proof. In the past the city has handed out packets of sterilizer for cisterns. A couple of tablespoons of unscented bleach will also sanitize the tanks, but using bottled water for drinking following either treatment is recommended.

The city of La Paz has announced an aggressive spray program in the hopes of averting an outbreak of Dengue fever. Fumigation by malathion will be increased in the evening hours in select neighborhoods. In the past public announcements of neighborhoods to be sprayed has appeared in advance on the radio and newspapers, in español of course. This action is to avert an outbreaks of Dengue following late in the season rains delivered by tropical rains and cyclones.

ORIGINAL News Story: Every year, following the rains, it is important to clear your property of standing water and screen your septic vents. Dengue usually runs in 7 year cycles and it has been 7 years since the last serious outbreak in Baja Sur. Dengue is a mosquito-borne infection which, in recent years, has become a major international public health concern.

Care should be taken to avoid contracting mosquito bites that can lead to infection. Spraying operations are now active in many parts of the city of La Paz and surrounding suburbs. Several deaths has been reported. Dengue is a serious disease, that poses the greatest threat to the very young, elderly and those under treatment for other diseases, which may compromise the bodies ability to resist infection.

Dengue Fever is found in many tropical sub-tropical regions in Mexico and around the world, predominantly in urban and semi-urban areas. Dengue viruses are transmitted by infected Aedes mosquitoes, (Aedes albopictus) which are most active during the day but can be found at night. There is no truth to the rumor that only a species of daytime mosquito carry the virus. The Asian Tiger Mosquito is denoted by the black and gray stripes on the abdomen and is know for its ability to bite quickly, more quickly that it can be swatted away…

There are four variations of Dengue fever, and you can only contract each version once, as the body develops antibodies to the virus. Unfortunately, as anyone who has had any of the varieties will tell you, once is enough. There are no medications for the disease, antibiotics are ineffective and may only prevent secondary infections and further reduce the bodies ability to combat the disease. Hospitalization can be required and intravenous fluids administered to prevent dehydration, a major threat of the infection.

HISTORY:  The first reported epidemics of Dengue occurred in 1779-1780 in Asia, Africa, and North America.  The near simultaneous occurrence of outbreaks on three continents indicates that these viruses and their mosquito vector have had a worldwide distribution in the tropics for more than 200 years.

A pandemic of dengue began in Southeast Asia after World War II and has spread around the globe since then.  Epidemics caused by multiple serotypes (hyperendemicity) are more frequent, the geographic distribution of dengue viruses and their mosquito vectors has expanded, and DHF has emerged in the Pacific region and the Americas. In Southeast Asia, epidemic DHF first appeared in the 1950s, but by 1975 it had become a frequent cause of hospitalization and death among children in many countries in that region.

The city of La Paz distributes packets of pesticides beginning late each summer, following our torrential rains, to homeowners and encourages removal of standing water. The standing water is a key link in the development of the mosquito responsible for transmission of the disease. Night time spray trucks have been seen throughout the city in an effort to contain the adult mosquito. Dengue is usually most prevalent in this area from late July to mid Nov.

The classic symptoms of Dengue Fever include a high fever that may last from 5 to 16 days; intense headache; eye, joint and muscle pain; and a rash. The rash typically begins on the arms or legs three to four days after the beginning of the fever. Symptoms can range widely in severity. Significant symptoms usually resolve within 2-4 weeks, but like Malaria, lethargia and some other symptoms can stay with the victim for months.

Dengue Hemorrhagic Fever is the most serious form of this illness. Individuals with Dengue Hemorrhagic Fever experience blood clotting problems which result in bleeding and shock (extremely low blood pressure). Hospitalization is usually required.

Dengue Fever is diagnosed by clinical symptoms and by specific blood tests.  There is no curative treatment for Dengue Fever. If there are no complications, recovery will occur within 2-6 weeks. Hospital care with intravenous fluids is usually necessary for individuals with the more serious Dengue Hemorrhagic Fever.

An individual infected with Dengue Fever is not directly infectious to other individuals except through sharing of blood contaminated needles. Untreated individuals, if bitten by Dengue Fever-capable mosquitoes, could infect a small number of mosquitoes. These could transmit Dengue Fever if they subsequently bite another human at least 1 to 2 weeks later, depending upon environmental conditions.  The best tactic to prevent Dengue is to avoid being bitten by mosquitoes. This includes sleeping in areas screened from mosquitoes, wearing long sleeves and pants, and using mosquito repellents.  There is no vaccine which can prevent Dengue Fever, however such vaccines are in development.

Alternate Names: Breakbone Fever, Dengue Disease, O’nyong-Nyong Fever

MosquitoWhy mosquitoes bite some people and not others…


To start, there are over 150 different species of mosquitoes, and they differ in biting persistence, habits, ability to transmit disease, and even flying ability.

Mosquitoes in Baja of the genus Aedes, which includes A. aegypti and A. albopictus, the Asian Tiger mosquito. Both can transmit Yellow Fever and Dengue Fever. Aedes mosquitoes feed early in the morning as well as at dusk and into the evening. They might also bite you during the day if it’s cloudy or if you wander into a shady place. Fortunately, they probably won’t enter your house – but they do prefer biting humans over other animals, and they are very strong fliers.

The different genera differ slightly in what attracts them to hosts they wish to bite. Mosquitoes use carbon dioxide, heat, moisture, scent, and even vision to locate hosts. When they are sniffing us out, they hone in on a large number of chemicals. A 2000 study identified 346 chemicals from human hand odors, of which 277 were potential mosquito attractants.

The most significant chemicals mosquitoes use to locate us and bite us include l-lactic acid, ammonia, carboxylic acids, and octenol, in combination with one another. In experiments, scientists found that adding l-lactic acid to the scent of an unattractive person made them more attractive to Aedes aegypti mosquitoes, and vice versa. Additionally, the presence of carbon dioxide makes A. aegypti mosquitoes more sensitive to human skin odors.

Yet another component of human odor is genetic. Although some theorize that individuals mosquitoes find unattractive simply produce less in the way of attractants, an alternative theory asserts that they produce components that interfere with mosquitoes’ ability to find their hosts. In fact, a 2008 study identified five such chemicals produced by humans found unattractive to mosquitoes.

For those looking to avoid toxic chemicals like DEET or permethrin (a possibly carcinogenic insecticide frequently used to treat clothing and mosquito nets), plants might hold the key to repelling mosquitoes. One of the most often cited is lemon eucalyptus. In fact, a 2014 Australian study found that a mixture of 32 percent lemon-eucalyptus oil provided more than 95 percent protection from mosquitoes for three hours, compared to a 40 percent DEET repellent that gave test subjects 100 percent protection for seven hours.

But lemon eucalyptus is not the only option. A 2013 study examined the ability of 20 different plant essential oils to repel malarial mosquitoes. Notably, the three best were cinnamon, citronella, and thyme, which were repellent, irritating, and toxic to the mosquitoes. Additionally, they found that cumin, lemongrass, coleus, and thyme were irritants to the mosquitoes at all concentrations. Another 2013 study found that cinnamon repelled the Asian Tiger mosquito, and so did a plant called Herba Schizonapetae that is used in Chinese medicine. Yet another plant that proved effective in studies is Nepeta parnassicus, a species in the mint family related to catnip.